For dermatoscopic examination for early diagnosis of malignant melanoma. Also for the examination of non-melanocytic lesions, basal cell carcinoma and dermatofibroma.
The skin surface refracts the light and partially reflects it. Thats why either an immersion liquid between the dermatoscope and the skin (for example dermatoscopy oil) or polarised light is needed to observe pigment cells or other structures in the deeper skin layers.